<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <style media="screen">
      #little_image {
        width: 400px;
        height: 400px;
        position: absolute;
        top: 0px;
        left: 0px;
      }
      #image {
        display: block;
        width: 400px;
        height: 400px;
        position: absolute;
      }
      #big_image {
        width: 500px;
        height: 500px;
        border: 1px solid grey;
        overflow: hidden;
        display: none;
        position: absolute;
        top: 0px;
        left: 400px;
      }
      #images {
        display: block;
        width: 1000px;
        height: 1000px;
        position: absolute;
      }
      #slider_block {
        width: 200px;
        height: 200px;
        position: absolute;
       
        border: 1px solid lightgrey;
        cursor: all-scroll;
        display: none;
      }
    </style>
  </head>
  <body>
    <div id="little_image">
      <img src="../Pictures/Camera Roll/枫叶.jpg" alt="" id="image"/>
      <div id="slider_block">
      </div>
    </div>
    <div id="big_image">
      <img src="../Pictures/Camera Roll/枫叶.jpg" alt="" id="images"/>
    </div>
  </body>
  <script type="text/javascript">
    var littleImage = document.getElementById('little_image');
    var bigImage = document.getElementById('big_image');
    var sliderBlock = document.getElementById('slider_block');
    //为littleImage添加鼠标移入事件
    littleImage.onmousemove = function(event) {
      event = event || window.event;
      sliderBlock.style.display = "block"; //移入鼠标显示sliderBlock
      bigImage.style.display = "inline-block";    //移入鼠标显示bigImage
 
      // 1、限定sliderBlock的活动范围
      var disX = event.clientX - sliderBlock.offsetWidth / 2;      //鼠标点击位置－移动块宽度的1/2
      var disY = event.clientY - sliderBlock.offsetHeight / 2;
     //最大移动位置就是little_image的宽度－移动块的宽度
      var distenceMaxX = littleImage.offsetWidth - sliderBlock.offsetWidth; 
      var distenceMaxY = littleImage.offsetHeight - sliderBlock.offsetHeight;
      if (disX < 0) {
        disX = 0;
      } else if (disX >= distenceMaxX) {
        disX = distenceMaxX
      }
      if (disY < 0) {
        disY = 0;
      } else if (disY >= distenceMaxY) {
        disY = distenceMaxY;
      }
      // 2、通过改变sliderBlock的left和top的指来让sliderBlock随着鼠标移动
      sliderBlock.style.left = disX + "px";
      sliderBlock.style.top = disY + "px";
      // 3、通过计算sliderblock在littleImage的比例，计算bigImage在大图中显示的比例
      var scaleX = disX / distenceMaxX;  
      var scaleY = disY / distenceMaxY;
      var images = document.getElementById('images');
      bigImage.scrollLeft = (images.offsetWidth - bigImage.offsetWidth) * scaleX;
      bigImage.scrollTop = (images.offsetHeight - bigImage.offsetHeight) * scaleY;
    }
     //添加鼠标移出事件
    littleImage.onmouseleave = function() {
      sliderBlock.style.display = 'none';   //  sliderBlock隐藏
      bigImage.style.display = 'none';      //  bigImage隐藏
    }
  </script>
</html>